Field of the Invention
The present invention relates to a depth information acquisition apparatus, an image pickup apparatus, a depth information acquisition method, and a program.
Description of the Related Art
Conventionally, as a depth information acquisition method of indicating a depth to a subject in an image, an acquisition method using a Depth from Defocus (DFD) method has been proposed, as disclosed in Japanese Patent Application Publication No. H1-167610. In a DFD method, a plurality of images having different blur are captured by controlling the imaging parameters of the imaging optical system, and the correlation value of the blur between a plurality of captured images is calculated by using a processing object pixel, and peripheral pixels thereof, in the plurality of captured images. This correlation value of the blur varies with the depth to the subject in the image. In a DFD method, depth information is acquired from the blur correlation value, on the basis of the relationship between the blur correlation value and the distance. In a DFD method, it is possible to acquire depth information by one imaging system. Therefore, a depth information acquisition method based on a DFD method is advantageous in that it can be incorporated into a commercially available image pickup apparatus.
Furthermore, Japanese Patent Application Publication No. 2010-016743 discloses an apparatus that calculates a correlation value of the blur in pixel units, for each pixel in a processing object region, from a plurality of images having different blur that are captured using different imaging parameters.
However, the brightness and chromaticity of the image also vary if the image is blurred. In the method disclosed in Japanese Patent Application Publication No. H1-167610, the correlation value of the blur between a plurality of images depends on the brightness and the chromaticity of the images, and the accuracy of the acquired depth information declines depending on the image.
In view of problems of this kind, in the method disclosed in Japanese Patent Application Publication No. 2010-016743, the accuracy of the acquired depth information is raised by setting a weighting coefficient for each pixel unit, for the blur correlation value, and finding a weighted average of the blur correlation value on the basis of the weighting coefficients. However, since the brightness and the chromaticity of the image changes with the blur, then it is difficult to set an optimal weighing coefficient for each pixel unit, and it has been difficult to satisfactorily suppress variation in the correlation value that is dependent on the spatial frequency of the subject. Therefore, it has been difficult to acquire highly accurate depth information.